In a More Electric Vehicle (MEV), the electrical system starting, generation, conversion and distribution system should serve several new functions to properly meet the power supply requirements of the more electric utilization systems and equipment. MEV architectures have been proposed to shift the primary motive power sources used for systems and services from pneumatic (engine bleed) and engine driven hydraulic sources to engine driven electric sources. In order to supply these systems in the most efficient manner, the electrical system should take on a configuration that differs from conventional vehicles. In one configuration, electrical generators can be fixed frequency, arrived at by using some type of hydro mechanical or electronic means to convert the varying speed of the propulsion engine into fixed (e.g., 400 Hz) frequency AC electrical power. Alternately, the generator can be connected directly to the engine gearbox, without the frequency converting equipment, and allowed to vary its output frequency within predetermined limits defined by the engine speed and gearbox ratio.
Although variable frequency (VF) has been frequently used on turbo propeller aircraft in the past to produce narrowband VF power, turbofan engines are only now adopting VF as technology advancements remove the previous concerns about wideband VF. Motor controllers are being developed to adapt the relatively wideband (2:1) VF that is characteristic of the turbofan engine speed range into more appropriate and efficient drive power for speed sensitive motors. As wideband VF becomes more prevalent, industry is also responding with more wideband frequency tolerant passive equipment (i.e., equipment that does not require active input quality conditions). Benefits of the VF generators are that they significantly reduced complexity as compared with their fixed frequency counterparts, and this simplicity translates into more efficient, lower weight and higher reliability power generation systems for new aircraft or other vehicle designs. This works well on a MEV with the concept of electrically starting the engines since the variable frequency generator design is the most suitable configuration to enable the generator to be configured by an external motor controller as a starting motor.
Another change in electrical power system design is the movement to “double voltage” (e.g., 230/400 VAC) generators to reduce generator and wiring weight in the vehicle. Since the MEV makes significant use of motor controllers and motor controllers that switch high voltage DC power to synthesize a driving power source for the various motors, the double voltage supply is preferable for creating a HVDC (typically, ± 270 VDC) source through relatively simple rectification methods. Therefore, the electrical systems of the future should be able to supply the electrical power types required by the new MEV components and systems while continuing to support traditional 115/200 VAC and 28 VDC services. Another challenge for the MEV electrical system results from the higher criticality and availability of electrical power required by the systems and services that it supports. As more systems move from pneumatic and hydraulic power supplies, the electrical system becomes the single source of motive force for those systems.
The inventor of this application has recognized that current drawbacks/needs can be addressed by providing an electrical system that ensures that sufficient redundancy and reliability are designed into the architecture to meet the safety considerations for the utilization equipment. Furthermore, the inventor of this application has further recognized that current drawbacks/needs can be addressed by providing an MEV electrical system architecture of robust design, which provides the high criticality and high availability service desired.